1. Field of the Invention
The present invention relates to organic compounds and an organic electroluminescent (EL) device, and more particularly, to compounds having molecular components capable of transporting/injecting hole and an organic EL device having a self-assembled monolayer comprising the same.
2. Description of the Related Art
In general, an organic EL device is formed by sequentially depositing a transparent electrode, a hole transport layer, a light emitting layer, an electron transport layer and a metal electrode on a substrate in a high vacuum. When the transparent electrode and the metal electrode are connected to positive (+) and negative (−) terminals of a power source, respectively, holes are supplied to the hole transport layer and the light emitting layer through the transparent electrode and electrons are supplied to the electron transport layer and the light emitting layer through the metal electrode. The holes and electrons supplied to the light emitting layer are combined in the light emitting layer to form excitons. The excitons drop to a ground state and generate light corresponding to a band gap of a light emitting polymer, thereby emitting light. Thus, when injected holes and electrons are balanced, the maximum luminescence efficiency can be exhibited. Since an organic EL device is quick at response speed and is of a spontaneous electroluminescence type, there is no need for back light, thereby attaining a lightweight, smaller device. Also, the organic EL device has several advantages such as excellent luminance and independence on an angle of field.
To date, various researches and suggestions to methods for improving the performance of organic EL devices have been made. In view of luminescent material preparation, new methods for providing high luminous efficiency and purity have been proposed. In view of device formation, researches into new structures of devices, cathode materials and improved ITO (indium tin oxide) film surface have been carried out. In particular, physically and chemically improving the surface of an ITO film considerably affects the performance of an organic EL device.
Changes in work function and surface roughness of an ITO substrate and a change in characteristics of an organic EL device according to surface treatment are described in J. Appl. Phys. Vol. 84, pp 6859-6870, in which surface treatment such as ITO substrate cleaning or plasma treatment is suitably performed to improve the performance of the device.
Also, formation of a self-assembled monolayer on an ITO surface using carboxylic acid is described in WO 99/07028, Adv. Mater., Vol. 11, pp 112-115, and Euro, Phys. J. B., Vol. 11, pp. 505-512. According to this method, the self-assembled monolayer can change a work function of ITO and can improve adhesion between an ITO surface and an organic film. In this method, the work function of ITO is changed according to the polarization direction of polar materials on the surface. However, the self-assembled monolayer using carboxylic acid is poor in view of stability against heat and stability over time.
Marks, et al. described that the performance of an organic EL device can be improved by spin-coating a hole transport material having 3 siloxanes or forming a thin film on an ITO surface by a self-assembled monolayer method, in U.S. Pat. No. 5,834,100, Adv. Mater., Vol. 11, pp 730-734, and Langmuir, Vol. 17, pp 2051-2054. However, according to this technique, since a compound having two or more silane groups is used, it is difficult to obtain a thin film having a uniform thickness, resulting in increased roughness.